1. Field of the Invention
The present invention relates to a stable fluid water-in-oil emulsion and to its use in the cosmetics, dermatological, veterinary and/or farm-produce fields. It can be provided in the form of a white or colored cream intended in particular for caring for the skin, make up for the skin, mucous membranes or for protection from the sun of the skin or mucous membranes, as well as for the preparation of a cream intended for the treatment of diseases of the skin and/or mucous membranes.
2. Discussion of the Related Art
In the cosmetics field, it is common to use creams composed of a water-in-oil (W/O) emulsion containing an aqueous phase dispersed in an oil phase. These emulsions contain a continuous oil phase and, thus, make it possible to form a lipid film on the surface of the skin which prevents transepidermal water loss and protects the skin from external attacks. These emulsions are particularly appropriate for protecting and nourishing the skin and in particular for treating dry skins.
These emulsions frequently present problems of stability, making their manufacture difficult. Various means have consequently been envisaged for overcoming this disadvantage. One means comprises the incorporation in the oil phase of an emulsion of fatty substances which are solid at room temperature, such as waxes or waxy compounds, silicas or modified clays, with the aim of thickening the continuous phase. However, this results in creams being obtained which are often dense and heavy.
Another means of overcoming the instability of W/O emulsions is the incorporation of an inorganic electrolyte, such as magnesium sulphate, which stabilizes the emulsion by the effect of electrostatic repulsion, preventing the phenomena of coalescence of the dispersed water globules. The absence of electrolyte increases the risks of instability of the emulsion, which is often reflected by a phase separation of the two phases. However, the presence of electrolyte can have disadvantages because it transpires that certain compounds which are desirable to use in these emulsions, are incompatible with electrolytes. It is known, for example, that anionic active ingredients form insoluble salts in the presence of inorganic electrolytes and end up precipitating more or less rapidly in the emulsion. Mention may be made, as anionic active ingredient of this type, for example, water-soluble UV screening agents, such as terephthalylidenedicamphorsulphonic acid or 4-benzophenone.
In addition, it is possible to overcome the instability of W/O emulsions by greatly increasing the emulsifier content of these emulsions. It is known, however, that emulsifiers used in a large amount can prove to be irritating to certain types of skin. Moreover, the creams obtained as described above, are often dense and heavy.
For the foregoing reasons, there remains a need for a water-in-oil emulsion which does not exhibit the disadvantages encountered with those known to date, this emulsion being stable even in the presence of an active ingredient sensitive to an electrolyte and/or in the absence of an electrolyte and/or of a solid fatty substance.